Ornamental Values of Continuously Cultivated Tulips Determined Using Principal Component Analysis

  Objective  Continuous cultivation by keeping tulip bulbs in ground for additional season to replace the wasteful and costly conventional practice was evaluated according to the ornamental value of the plants under treatment.

  Method  Thirty-six Dutch tulip cultivars were planted for two consecutive years without digging out the bulbs in the autumn prior to 2^nd year growth as handled by the conventional practice. Aboveground phenotypic traits including plant height, basal leaf number, length of the longest leaf, length of the shortest leaf, width of the longest leaf, width of the shortest leaf, flower diameter, length of petal, and length of flower stem of the plants were measured in two years and followed by a principal component analysis on the data.

  Result  The sprouting of the 36 cultivars after one year of cultivation showed a rate ranging from 16.51% to 86.68%. The reduction of the new shoot emerging rate was between 7.14-82.10%, with 17 cultivars less than 40% on the decline. The statistical analysis indicated 9 traits (i.e., plant height, basal leaf number, length of the longest leaf, length of the shortest leaf, width of the longest leaf, width of the shortest leaf, flower diameter, length of flower stem, and leaf area) to be the principal components for the ornamental evaluation. Of the 36 cultivars, 55.5% ranked with upgraded scores after the continuous cultivation and 19.4% downgraded. Taking sprouting rate, evaluation score, and number of increased or decreased phenotype rank into consideration, the 6 cultivars with high and stable ornamental value were Yellow Pomponette, Negrita, Leen Van Der Mark, Christmas Marvel, Pink Pomponette, and Parade.

  Conclusion  Six tulip cultivars were considered suitable for continuous tulip horticulture in Xining and/or areas with similar environmental and climatic conditions.